Apparatus for mounting a plurality of magnet segments on a back ring

ABSTRACT

A method and apparatus for assembling permanent magnet segments and a back ring wherein a fixture hold segments in circumaxially spaced relationship, adhesive is applied to the segments, externally from pressure sensitive adhesive tape and the fixture then expands to urge the segments into firm bonding engagement with the back ring.

This is a divisional application of U.S. patent application Ser. No.10/674,832 filed Sep. 29, 2003, now U.S. Pat. No. 6,974,522.

BACKGROUND OF INVENTION

In the manufacture of permanent magnet motors, magnet segments areconventionally secured in circumaxially spaced relationship on theinterior surfaces of cylindrical back rings in a manual operationemploying a two-part epoxy. The assembled magnet segments and rings arethen conventionally encapsulated in an injection molding operation.

While generally satisfactory, the procedure is a slow and tedious stepin the manufacturing process and the epoxy is both expensive anddifficult to apply.

Accordingly, it is a general object of the present invention to providean efficient and more expeditious method and apparatus for assemblingmagnet segments on a back ring.

A further object of the invention is to provide an assembly method andapparatus which requires minimal manual intervention and which exhibitsa high degree of consistency and repeatability in the results achieved.

SUMMARY OF THE INVENTION

In fulfillment of the aforementioned objects and in accordance with thepresent invention, a rotatable expandable and contractible fixture isprovided and the magnet segments are releasably secured on and about thefixture in circumaxially spaced relationship with their exteriorsurfaces outwardly exposed and provided with an arcuate configurationsubstantially conforming to that of the interior surface of the backring. Preferably, a liner backed pressure sensitive adhesive tape knownas an “adhesive transfer tape” is then employed with a means forapplying the adhesive sequentially to the magnet segments during fixturerotation. The liner is separated during application of the adhesive tothe segments. Relative axial movement is then effected between thefixture carrying the segments and the back ring to enter the formerwithin the latter. Expansion of the fixture follows urging the magnetsegments firmly into engagement with the interior surface of the backring and bonding them in position thereon. The fixture is thereaftercontracted and relative axial movement is again effected between thefixture and the back ring to remove the former from the interior of thering assembly.

Apparatus employed in the practice of the foregoing method in additionto the fixture and adhesive applying means which preferably comprises anapplication roller includes a vacuum source for releasably securing themagnet segments on the fixture, a rotary drive means preferably in theform of a step motor for the fixture, locating surfaces on the fixtureand an opposing device resiliently urging the segments against thesurfaces to precisely locate the same, a liner take-up roll, and otherauxiliary devices.

DRAWINGS

FIG. 1 is a top view of an assembled back ring and six (6) magnetsegments.

FIG. 2 is a cross sectional view taken generally as indicated at 2-2 inFIG. 1

FIG. 3 is a somewhat schematic exploded perspective showing a rotatablefixture, a drive motor and vacuum pump therefore, and a collet-likeexpander associated therewith.

FIG. 4 is a side view showing the fixture of FIG. 3 with a single magnetsegment mounted thereon.

FIG. 5 is a somewhat schematic perspective view showing the fixture witha single magnet segment thereon and a device which operates to preciselylocate the segments axially on the fixture.

FIG. 6 is a somewhat schematic perspective view showing the majority ofthe major components of the apparatus of the invention.

FIG. 7 is a perspective view showing a rotatable turret carrying a“bumper” for axially locating the segments and a gripper for placingback rings about fixtures carrying adhesive bearing segments.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring particularly to FIGS. 1 and 2, it will be observed that six(6) permanent magnet segments 10,10 are provided in the preferredembodiment of the invention shown. The magnet segments 10,10 are equallyspaced circumaxially as shown and are mounted on the interior surface ofa cylindrical back ring 12. The segments may be metallic or ceramic andthe back ring is conventionally of iron. Exterior surfaces 14,14 of themagnet segments are arcuate to conform substantially with the interiorsurface of the back ring 12. The interior surfaces of the segments areflat as shown and presently preferred for engagement with similar flatsurfaces 16,16 on a fixture 18 best illustrated in FIG. 3.

The fixture 18 has six (6) flat surfaces 16,16 respectively forreceiving the six (6) magnet segments 10,10. Each of the flat surfaceshas a pair of vacuum ports 20,20 connected by suitable conduits (notshown) to a vacuum source which may comprise a conventional vacuum pumpat 22. An appropriate computer controlled valve system (not shown)provides for the establishment and removal of a vacuum at the ports20,20 suitably timed respectively to secure and release magnet segmentsfrom the surfaces 16,16. A step motor 24 rotates the fixture also intimed relationship with other elements of the apparatus under computercontrol.

Disposed within and forming a part of the fixture 18 is an axiallymovable collet-like member indicated generally at 26 and which has six(6) flexible fingers 28,28. The fingers co-operate with radiallyinwardly biased pins 30,30 which project through openings 32,32 in thefixture 18 to engage magnet segments and urge the same outwardly forengagement with and bonding to an associated back ring. A pneumaticcylinder 34 operates the collet axially under computer control, toexpand and contract the pins as required.

A locating device best illustrated in FIGS. 3 and 7 includes radiallyextending locating surfaces 36,36 on six (6) small projections 38,38 onthe fixture 18, one for each magnet segment 10,10. At an opposite end ofthe fixture six (6) resiliently mounted “bumpers” 40,40 are moveableaxially toward and away from the segments to urge them into engagementwith the locating surfaces 36,36 and precisely position the sameaxially. The bumpers may also be pneumatically operated under computercontrol.

FIG. 4 shows a single magnet segment 10 mounted on a fixture 18 andengaged by a pair of “grippers” 42,42 which have long narrow fingers43,43 operable to locate and hold the segment. The “grippers” may alsobe pneumatically operated under computer control.

In FIGS. 6, and 7 components of the apparatus of the invention areillustrated. A fixture 18 with six (6) magnet segments mounted thereonis positioned adjacent an adhesive applying means indicated generally at44 and comprising an application roller 46 about which an adhesive linertape 48 is directed from an adhesive storage reel 50. An intermediateroller 52 directs the tape from the storage reel 50 to the applicationroller 46 where it is resiliently urged against the magnet segments bypneumatic means indicated generally at 53. Friction created at theinterface between the adhesive bearing tape and the rotating magnetsegments serves to drive the apparatus with the tape being thus drawnfrom its storage reel 50 and about the rolls 46 and 52. A take-up reel54 receives the liner 48 a which separates from the adhesive at theinterface between the magnet segments and tape at the application roll46 and is over driven by a timing belt 56 extending from the frictiondriven application roller. A small friction clutch 58 accommodates thevariation in speed as the tape reel 50 becomes smaller and the linertake-up reel 54 becomes larger.

In operation, the fixture is rotated through 345° and then stopped. Apneumatically operated brake 60 stops the tape dispensing reel 50 andthe fixture 18 is then rotated an additional fifteen degrees (15°) tobreak the adhesive. The application roller 46 then backs off. At thispoint, it should be noted that a blank area is thus created on the liner48 a. This of course results in a loss of the necessary friction torotate the application roller 46, supply reel 50 etc. Accordingly, anindex arm over with a needle-roller clutch is provided to advance thetape as the application roller moves forward for a succeeding adhesiveapplying sequence.

Once the adhesive has been applied, the back ring and the fixturecarrying the segments are moved relatively in an axial direction toassemble the elements as best illustrated in FIG. 7. Turret 54 isrotatable and movable vertically to alternately present the “bumpers”40,40 and a back ring gripper 56 to the fixture 18. As shown, the“bumpers” 40,40 are elevated prior to a segment loading operation. Theyare subsequently lowered to precisely locate the segments and thenraised prior to turret rotation. When the turret has been rotated, theback ring 12 is placed about the adhesive carrying segments and thecollet 26 urges the pins 32,32 outwardly and the segments against theback ring to bond the same in the desired positions thereon.

As indicated above, the assembly may then be over molded in an injectionmolding operation.

In practicing the method of the invention with the afore describedapparatus, the segments are mounted on the fixture, adhesive is appliedto the segments, the fixture carrying the segments is assembled with theback ring, and the segments are urged into firm bonding engagement withthe ring.

1. Apparatus for assembling a plurality of magnet segments on aninterior surface of a cylindrical back ring for incorporation in apermanent magnet electric motor, the magnet segments each having anarcuate outer surface substantially conforming to the interior surfaceof the back ring, comprising an expandable and contractible fixtureadapted to receive and hold the magnet segments in the desiredcircumaxially spaced arrangement with their exterior surfaces exposed, asupply of adhesive tape, a means for applying the adhesive from the tapesequentially to the outer surface of the magnet segments by rotating thefixture, a means for pressing the segments bearing adhesive against theinterior surface of the back ring by expanding the fixture so as to movethe magnet segments radially outwardly and thus bonding the magnetsegments to the back ring, and contracting the fixture to enablewithdrawal of the fixture from the ring and segments.
 2. The apparatusaccording to claim for assembling a plurality of magnet segments on aninterior surface of a cylindrical back ring for incorporation in apermanent magnet electric motor as set forth in claim 1 wherein a meansfor rotatably driving the fixture is provided, and wherein the fixtureis thus rotated to apply adhesive sequentially to the magnet segments.3. The apparatus according to claim for assembling a plurality of magnetsegments on an interior surface of a cylindrical back ring forincorporation in a permanent magnet motor as set forth in claim 2wherein said adhesive applying means takes the form of an applicationroller about which the adhesive tape extends and a means for resilientlyurging the roller toward the magnet segments.
 4. The apparatus accordingto claim for assembling the adhesive a plurality of magnet segments onan interior surface of a cylindrical back ring for incorporation in apermanent magnet electric motor as set forth in claim 3 wherein theadhesive tape takes the form of an adhesive transfer tape having a linerwhich is separated from the adhesive as it is applied to the segments.5. The apparatus according to claim for assembling a plurality of magnetsegments on an interior surface of a cylindrical back ring forincorporation in a permanent magnet electric motor as set forth in claim4 wherein a rotatably driven take-up roller is provided to receive theliner after separation of the same from the adhesive.
 6. The apparatusaccording to claim for assembling a plurality of magnet segments on aninterior surface of a cylindrical back ring for incorporation in apermanent magnet electric motor as set forth in claim 2 wherein axiallocating surfaces are provided on the fixture and wherein a device isprovided at an opposite end of the fixture to urge the magnet segmentsagainst said surfaces and thereby precisely locate the same axially. 7.The apparatus according to claim 6 wherein an axially movable rotatableturret is provided and carries said device for urging the magnetsegments axially and a gripping device for holding the back ring, saidturret being rotated and moved axially to alternately urge the magnetsegments axially against their respective axial locating surfaces and toplace the back ring about the fixture loaded with the adhesive-carryingmagnet segments.
 8. The apparatus according to claim for assembling aplurality of magnet segments on an interior surface of a cylindricalback ring for incorporation in a permanent magnet electric motor as setforth in claim 2 wherein a vacuum means is provided for releasablysecuring the magnet segments on the fixture.
 9. The apparatus accordingto claim for assembling a plurality of magnet segments on an interiorsurface of a cylindrical back ring for incorporation in a permanentmagnet electric motor as set forth in claim 8 wherein individualgrippers are provided respectively for each magnet segment to assist thevacuum means in properly positioning the magnet segments on the fixture.10. The apparatus according to claim for assembling a plurality ofmagnet segments on an interior surface of a cylindrical back ring forincorporation in a permanent magnet electric motor as set forth in claim2 wherein the fixture includes a collet like device operable to expandand force the magnet segments against the interior surface of the backring, and thereafter operable to contract and release the same.